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Looks like heavy float chamber castings - to change the natural vibration frequency of the solid mounted carbs ?
Wonder if the carb bodies and mounts stood up to the extra weight...

The early version has swill pots fitted which is not common. Main float chamber is very far forward of the mainjet, the additional swill pot effectively makes the mainjet central in a "virtual bowl". Should eliminate problems caused by fuel surge on acceleration or braking.

Looks like heavy float chamber castings - to change the natural vibration frequency of the solid mounted carbs ?
Wonder if the carb bodies and mounts stood up to the extra weight...

The early version has swill pots fitted which is not common. Main float chamber is very far forward of the mainjet, the additional swill pot effectively makes the mainjet central in a "virtual bowl". Should eliminate problems caused by fuel surge on acceleration or braking.

I have always appreciated Jawa designs, which is more than I can say for this contraption. I find it hard to believe that it came out of the Jawa factory looking like this.
So I doubt that it is a works Jawa.

I have always appreciated Jawa designs, which is more than I can say for this contraption. I find it hard to believe that it came out of the Jawa factory looking like this.
So I doubt that it is a works Jawa.

So do I. The engine is a road single cam version. You can see the flanges on the RHS of the crankcase for the road motor outer cover.
My guess is a home built special - with a nod to the works in the use of square tubing, lol.

Ken MacIntosh built a much nicer one for a customer. I've seen it written up in I think a Classis Bike mag Husa.
I remember going with my father to look at a road 500 Jawa thet he was negotiating to buy off a notorious hoarder here in ChCh.
The sale fell through which was a pity as it was a nice rarity in NZ.

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the edge make it almost look like a fabrication although it seems to be no weld near the std bowl

I reckon they're a pair of one-off castings. Looks to me like the pattern for the chamber has simply had a ring added to it.
They've been cleaned up after casting by machining the OD - but there's still a ragged edge there.
Given how hard a stepped pattern for the inside would be, I'm picking the add-ons are solid.

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I reckon they're a pair of one-off castings. Looks to me like the pattern for the chamber has simply had a ring added to it.
They've been cleaned up after casting by machining the OD - but there's still a ragged edge there.
Given how hard a stepped pattern for the inside would be, I'm picking the add-ons are solid.

I found some more pics
i are not convinced either way but as we have access to Jan he will know as it appears the IRZ carbs were used into his era with Derbi and mabye others. ")

Originally Posted by jamathi

That is true Frits.
But I had 2 cylinders cast with the bottom of the exhaust as high as the transfers top.
The last 5 years all our exhaust ducts were CNC machined.
With many variations!
During the last year the exhaust bottom was 3mm above BDC.

I have always appreciated Jawa designs, which is more than I can say for this contraption. I find it hard to believe that it came out of the Jawa factory looking like this.
So I doubt that it is a works Jawa.

I think those pics originated in Australia, where seems that it's up for sale at the moment - be in quick or you'll miss it! - Still as I said somewhere else a while ago .... I hate to see anyone's dream going down the gurgler, good or bad. ........ At least they tried and made an effort!

Freedom of speech is important but if what we say is considered incorrect by our peers, they will quickly put us right.
P.C. will eventually destroy our right to tell the truth.

I think those pics originated in Australia, where seems that it's up for sale at the moment - be in quick or you'll miss it! - Still as I said somewhere else a while ago .... I hate to see anyone's dream going down the gurgler, good or bad. ........ At least they tried and made an effort!

Fair enough Will. Either someone will buy it for what it is now or as the basis for a more conventional build. Some good bits in there.
Like the curate's egg - good in parts, LOL.

We've had similar things come up for sale here in NZ. I hate to see well - known NZ specials gutted for maybe a 7R or manx engine and box. The history is lost.

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Fair enough Will. Either someone will buy it for what it is now or as the basis for a more conventional build. Some good bits in there.
Like the curate's egg - good in parts, LOL.

We've had similar things come up for sale here in NZ. I hate to see well - known NZ specials gutted for maybe a 7R or manx engine and box. The history is lost.

Yes This sort of thing should definitely be preserved as near as possible to how it was originally conceived, (no matter what it might look like now!).
Usually these gems are left behind (under the bench) by some guy who was totally misunderstood by the family and when he passed on, the remaining family couldn't see beyond having a tidy garage! so out they went! They were after all only built to make a dream tangible if nothing else ......... Perhaps I'm drawing too much from my own experiences - I'm misunderstood too you see!-

But, here's a case in point!
He could be a great designer by now, a stuntman, a comedian, or manager of a big Corporation - One just never knows! - does one?

Look at a certain guy on our TV ads - He has a very successful Real Estate sales company and likes to be in all his his ads, the most recent one being about him turning up to the office on his road bike all immaculately dressed etc. - how many people would write him off as just another poser? - but then, how many people would realize that he was 350cc NZ champion (twice?). - you just never know! (probably wasn't him who built the machine in the picture though!).

Freedom of speech is important but if what we say is considered incorrect by our peers, they will quickly put us right.
P.C. will eventually destroy our right to tell the truth.

Motion to evict WilDun from KB henceforth due to savage and unprovoked visual assault on members delicate technical sensibilities!

EH? - Translation into modern English please! - That's how I was taught at school, but I dropped out and bought myself a bike (motorbike that is) instead! - Since then, I have always thought that was much better decision than staying on to learn bloody Shakespeare! - and ........ I'm really a very sweet and gentle person and those are all lies! so there! ....... I don't know - honestly!

Seriously, - You must admit that pic. does have a certain " no Bullshit" element about it!

Freedom of speech is important but if what we say is considered incorrect by our peers, they will quickly put us right.
P.C. will eventually destroy our right to tell the truth.

Yes This sort of thing should definitely be preserved as near as possible to how it was originally conceived, (no matter what it might look like now look like now!).
Usually left behind under the bench by some guy who was totally misunderstood by the family and when he passed on, the remaining family couldn't see beyond having a tidy garage! so out they went! They were after all only built to make a dream tangible if nothing else ......... Perhaps I'm drawing too much from my own experiences - I'm misunderstood too you see!-

Case in Point!
He could be a great designer by now, a stuntman, a comedian, or manager of a big Corporation - One just never knows! - does one?

I mean look at a certain guy on our TV ads - He has a very successful Real Estate sales company and likes to be in all his his ads, the most recent one being about him turning up to the office on his road bike all immaculately dressed etc. - how many people would write him off as just another poser? - but then, how many people would realize that he was 350cc NZ champion (twice?). - you just never know! (probably wasn't him who built the machine in the picture though!).

Is that from an albatross colony or something cause it covered in avian Guano